This invention relates to digital imaging systems. More particularly, this invention relates to digital imaging systems having multiple modules, and to methods for making such systems.
Solid state imaging systems are proliferating in a wide variety of imaging applications. Such systems have an array of photoresponsive elements fabricated in a semiconductor integrated circuit. The photoresponsive elements are disposed in a sensor array that typically is a rectangular grid. When the sensor array is exposed to an optical image, each photoresponsive element generates an analog electrical signal that is related to the amount of light striking it. Each such signal comprises a pixel of an electronic image corresponding to the optical image, and is usually subjected to further signal processing in an imaging application.
One type of solid state imaging system that has many advantages is a digital imaging system in which the signal processing circuitry associated with each photoresponsive element includes an analog-to-digital converter (xe2x80x9cADCxe2x80x9d) so as to produce a digital output signal that is responsive to the amount of light impinging on the photoresponsive element. An example of such a system is shown in U.S. Pat. No. 4,561,425, the contents of which are incorporated herein by this reference. In contrast to other digital imaging systems in which an ADC is time-shared among many photoresponsive elements, the digital imaging systems in which each photoresponsive element has its own ADC, or in which an ADC services only a few photoresponsive elements, require minimal handling of analog signals and enable more easily handled digital output signals to be provided for each pixel in the sensor array. Applicant refers to such systems as xe2x80x9cdigital pixel sensorxe2x80x9d or xe2x80x9cDPSxe2x80x9d systems.
Other functional elements of a digital imaging system may include a memory for storing image data, i.e., a frame buffer; processing circuitry for processing acquired image data or stored image data; input/output (xe2x80x9cI/Oxe2x80x9d) circuitry for inputting control signals and outputting image data; and control circuitry for controlling the operation of the sensor array, frame buffer, processing circuitry, and/or I/O circuitry. Some or all of these ancillary functional elements may be implemented in integrated circuitry formed in the same semiconductor die as the sensor array. Thus, one integrated circuit can include a substantial portion of the electronic circuitry necessary to implement a digital imaging system. In imaging, as in many areas of electronics, advances in semiconductor integrated circuit technology permit, and usually foster, integration of more and more functions in a single die.
One factor affecting the quality of a digital imaging system is the number of pixels (the xe2x80x9cpixel countxe2x80x9d) in the digital images it produces. If the surface area on a die devoted to each pixel remains constant, increasing the pixel count of an integrated circuit digital imaging system requires increasing the surface area of the die generally in proportion, at least in the area of the die containing the sensor array. Thus, for example, quadrupling the pixel count of a sensor array from 512xc3x97512 pixels to 1024xc3x971024 pixels might require roughly doubling the linear dimensions and quadrupling the area of the die. However, die linear dimensions and areas cannot be increased without eventually encountering drawbacks or limits. For instance, there is a limit to the size of die that can be produced using commercially available stepper photolithography equipment due to its fixed, relatively small exposure field. Although it may be expected that future improvements in integrated circuit fabrication technology will permit fabricating larger dies with increased pixel counts, such future improvements will not change the fact that there will still be limits of possible or practical pixel count in a digital imaging system fabricated as a single die; they will merely change what the limits are.
In accordance with the present invention, a digital pixel sensor-based modular digital imaging system includes several integrated circuit component modules. In one embodiment, the present invention t: is an imaging apparatus comprising a plurality of component modules disposed in a fixed spatial relationship, wherein each of the component modules includes at least one integrated circuit die, one or more of the component modules includes an integrated circuit die having an array of digital pixel sensors and a frame buffer, and one or more of the component modules includes an integrated circuit die having f: control circuitry and/or input/output circuitry. In another embodiment, the present invention is method of making imaging apparatus comprising disposing a plurality of component modules in a fixed spatial relationship on a substrate, wherein each of the component modules includes at least one integrated circuit die, one or more of the component modules includes an integrated circuit die having an array of digital pixel sensors and a frame buffer, and one or more of the component modules includes an integrated circuit die having control circuitry and/or input/output circuitry.
These and other objects and features of the present invention are set forth in greater detail in the following description and the drawings.